Printers, like page-wide-array printers and multi-pass printers, include a print bar having a print head or array of print heads. Usually, the print bar extends at least across the width of a print substrate (e.g. paper) in the case of 2D printers or a build material in the case of 3D printers. A print head comprises one or more nozzles for ejecting printing fluid (e.g. ink) to be printed onto the print substrate or, in the case of 3D printers, for emitting radiation (e.g. light) to interact with build material in order to generate a 3D print out. In the following, the term “print target” covers both a print substrate used in 2D printers and build material used in 3D printers. Likewise the term “print” applies to 2D printers and 3D printers, wherein in the latter case “print” covers a generation of 3D structures and the like being producible by a 3D printer.
In general, in a print process, the print bar and a print target are moved in relation to each other. For example, the print target may be moved relative to the print bar, which is not moved, like in the case of page-wide-array printers. It is also possible that the print target is not moved, while the print head is moved, like in the case of 3D printers.
Defects of single nozzles of a print head may result in printing artifacts. Movements of the print bar and the print target in relation to each other may result in different aging of the nozzles. Thus, some nozzles are more used than others and, hence, degrade faster. This may also lead to visible printing irregularities. To address these aspects, multi-pass printing may be used in page-wide array printers and 3D printers. In multi-pass printing overlapping portions of a print target are printed on multiple times, wherein the print target or the print head is moved forwards and backwards (i.e. in the opposite direction) in a “two step forward one step backward” style. Information on multi-pass printing used in page-wide array printers can be found in U.S. Pat. No. 8,057,010 B2.
Figures may show a print target for demonstration purposes. However, the print target is typically not a component of the printer.